background.js

(function (c) {
  c.runtime.onMessage.addListener(async function (
    request,
    sender,
    sendResponse
  ) {
    switch (request.type) {
      case "EVENT_1":
        // TODO: do something
        break;
      case "EVENT_2":
       // TODO: do something

        break;
      default:
        break;
    }

    return true;
  });

})(chrome);

popup.js

chrome.runtime.sendMessage({
  type: "EVENT_1",
  data: {hey: 'EVENT_1'},
});